Almost 30 years ago, polyunsaturated fatty acids (PUFAs) of vegetable origin (Omega-6) were found to have a hypocholesterolemic effect when substituted for saturated fat in the diet. In the early 1970's, Bang and Dyerberg observed a relative scarcity of coronary thrombosis among Greenland Eskimos which they were able to correlate to the diet of those Eskimos. The diet consisted of meat from Arctic mammals (seal and whale) as well as some fish. This provided them with a diet which included approximately 7 grams of Omega-3 fatty acids daily. These findings stimulated research into the impact of Omega-3 fatty acids on health in general. This led to the discovery that the Omega-3 series of fatty acids, and particularly eicosapentaenoic acid (hereinafter called EPA) (20:5 Omega-3) and docosahexaenoic acid (hereinafter called DHA) (22:6 Omega-3), have high pharmacological and dietary potential.
Recently, the potential advantages of the Omega-3 fatty acids derived from fish sources were reported in the New England Journal of Medicine, Volume 310, No. 19, pages 1205 through 1223, in papers by Kromhout et al., Phillipson et al. and Lee et al., May 9, 1985.
Fish oils containing EPA and DHA are manufactured by first mincing or cutting up the fish, cooking it for approximately 15 minutes at 90.degree. C., and then separating the crude oil, which can then be alkaline refined and bleached. The oil so produced may be winterized or hydrogenated depending upon its final use. Finally, the oil may be deodorized by vacuum steam distillation at high temperatures, usually above 200.degree. C.
Fish oils may be recovered from fish organs as well as from the meat of the fish. One such fish organ oil is cod liver oil, which has been used to improve health for decades, even though such oils are usually high in cholesterol, pesticides and heavy metals.
The fish oils processed as described above usually have a strong, highly objectionable fishy odor, plus a rancid odor and fishy flavor which are probably due to the autoxidation of polyunsaturated fatty acids and the deterioration of proteinaceous materials. In order to use the oil for edible and certain other purposes, it is necessary that the oil be deodorized.
Conventional deodorization processes involve the vacuum steam distillation of the oils at temperatures in excess of 200.degree. C. While this process removes volatile flavor compounds, the high temperature to which the oils are subjected during the deodorization process creates undesirable side reactions, such as the formation of polymers, conjugated dienes, trans-isomers and other positional isomers. Most important of all, the content of EPA and DHA in the oil is decreased due to thermal decomposition as well as due to the formation of polymers. Moreover, the resulting product has poor flavor stability and poor resistance to oxidation. Although such undesirable side reactions are avoided if the products are distilled at low temperatures, e.g., 60.degree.-100.degree. C., such low temperature processes do not remove the higher boiling volatiles and more polar flavor compounds. Moreover, the low temperature vacuum steam distillation will not remove the undesirable minor constituents, such as cholesterols, pesticides, etc.
When Omega-3 fatty acid-containing oils, such as fish oil, are deodorized according to the prior art at high temperatures in excess of 200.degree. C., certain chemical reactions will take place which would decrease the biological benefits of the oils. Moreover, the products of such chemical reactions may have adverse biological effects.
In the prestigious Tufts University Diet and Nutrition Letter (Vol. 5, No. 11, January 1988) it was reported that in analysis led by Dr. Ernest J. Schaefer, MD, Chief of the Lipid Metabolism Laboratory at the New England Medical Center, 10 major brands of fish oil capsules only contained an average of 38% of the EPA and 85% of the DHA that the companies claim are present. This is probably due to the loss of the biologically beneficial Omega-3 fatty acids with the formation of biologically harmful polymers during storage.
Another interesting observation is that during the deodorization according to prior art processs, at high temperatures, there is a tendency to form geometrical or positional isomers. The biological effects of these isomers to human health has been questioned in the literature.
The damages of prior art deodorization to fish oil are described quantitatively in detail in the Ph.D. dissertation submitted to Rutgers, The State University of New Jersey, in January, 1988, by Timothy J. Pelura. The title of the thesis is "The Effect of Deodorization Time and Temperature on the Chemical, Physical and Sensory Characteristics of Menhaden Oil".